Monitoring the effectiveness of a bio-fertilizer restoration technique using multi-resolution satellite and meteo-data: the case of Xylella fastidiosa subsp. Pauca

Xylella fastidiosa, subsp. pauca (Xfp), has attacked the olive trees in Southern Italy causing severe impacts on the agro-ecosystem services, such as provisioning, regulating and cultural. To reduce both the Xfp cell concentration and the symptom disease, a bio-fertilizer restoration technique has been used. Our study applied multi-resolution satellite data to evaluate the effectiveness of such restoration action at both field and tree scale. For field scale, a time series of High Resolution (HR) Sentinel-2 images, acquired in the months of July and August from 2015 to 2020, was employed. First, four spectral indices from treated and untreated fields were compared. Then, their trends were correlated to meteo-events. For tree-scale, Very High Resolution (VHR) Pléiades images were selected at the closest dates of the Sentinel-2 data to investigate the response to treatments of each different cultivar. All indices from HR and VHR images resulted higher in treated fields than in those untreated. The analysis of VHR indices revealed different cultivar response to treatments. The findings from HR data could be used to evaluate plant conditions at field level after treatments, while VHR imagery could be used to optimize treatment doses per cultivar. The findings in agreement with in-field PCR results.